Moved VERSION to a standalone file

Need to change version number in VERSION file
and also in src/sphinx/fjage_quickstart.sh
Cloners now called via reflection

This allows cloner jars to be absent if the specific cloner is not
used. Also added test cases to check that the cloners work correctly.
Documentation updates and small enhancements

DevGuide:
Completed behaviors chapter
Other minor fixes

Code:
- Message filters now check for inherited class rather than the exact
class
- Minor documentation fixes
- GroovyAgentExtensions are now enabled via a dedicated enable() method